Although a few big domestic cars avoid the guzzler tax because they are averaged in with smaller models, there is no question that Detroit has become serious about fuel economy.

But because the GTO is a passenger car, the rating is low enough to require buyers to pay a $1,000 guzzler tax.

G.M. officials, both in engineering and public relations, say the company had been operating under a clear directive, if not quite an iron-clad policy, to avoid making automobiles that would be subject to the guzzler tax.

Driven hurriedly, the M returned 17 m.p.g.; the E.P.A. rating - 16 m.p.g. in the city, 24 on the highway - earns it a $1,000 guzzler tax.

This trick gives the car a bump in the fuel-economy ratings, keeping it free of a guzzler tax, but that hardly justifies such an intrusive system - especially since owners routinely disable it with a $20 after-market part.

The Shelby's poor mileage wins it one distinction: a $1,300 guzzler tax.

The testing was mandated by the Energy Tax Act of 1978 in order to determine the rate of the guzzler tax that applies for the sales of new cars.

A weight average of city (55%) and highway (45%) fuel economies is used to determine the guzzler tax.

The Chinese government has been increasingly intent on energy conservation, imposing gas-mileage requirements on all models of cars, minivans and sport utility vehicles introduced after July 1, and preparing to impose gas- guzzler taxes, too.

The guzzler tax is applied first; the luxury tax adds insult to injury.